They are more likely to be arrested for possesion even though they use drugs at a similar rate than whites.
Ah yes, I knew you would bring this up, the 2011 National Survey on Drug Use and Health of black and white youths that shows that whites and blacks have similar drug use rates, it is commonly given as proof of how blacks are unfairly targeted. The problem is that the survey is highly misleading because first it counts alcohol as a drug. Yes white teens may binge drink more than black people, but that's hardly comparable to something like crack.
But more importantly its SELF-REPORTED data, which makes it completely unreliable. This self-reported survey of drug use has actually been completely debunked by academic research, which compared whether different races report using drugs in these surveys and then actually testing their urine samples to see if they are telling the truth. It found that blacks are 20 times more likely to lie about using cocaine:
"This study provides evidence that compared with other groups, African Americans provide less valid information on drug-use surveys. The findings suggest that African American respondents had significantly lower concordance rates"
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3455900/pdf/11524_2006_Article_433.pdf
The more accurate way is to look at the data provided by the US Department of Health, which releases reports every year on how many people came to the emergency room while on drugs. They find that blacks are 3.5X more likely to go to the ER because of elicit drugs and 7.2X more likely to go to the ER because they are using crack.
Black people are overwhelmingly targeted for drug offenses.
They dominate drug dealing offenses. Blacks make up for 40% of drug dealer related arrests:
"According to the federal Bureau of Justice Statistics, of the estimated 225,242 sentenced prisoners under state jurisdiction serving time for drug offenses in 2011, 67,271 were non-Hispanic white (29.9%), 91,775 were non-Hispanic black (40.7%), 47,479 were Hispanic (21.1%), and 18,717 (8.3%) were unaccounted for or not specified in the report."
http://www.bjs.gov/content/pub/pdf/p12ac.pdf
So while they make up only 12% of the population, they make up 40% of the drug dealers.